The present invention relates to a hinge for collapsible ladders, and more particularly, to a hinge for collapsible ladders having an improved structure in which a hinge spring for the collapsible ladders is not exposed externally.
Korean Utility Model Registration No. 1991-303 discloses a common hinge for collapsible ladders. As shown in FIGS. 1A and 1B, this conventional invention discloses the hinge having an auxiliary round plate 3xe2x80x3 disposed between a pair of round plates 3 and 3xe2x80x2. A rotary plate 11 contacts one side of the auxiliary round plate 3xe2x80x3 by a flange 11xe2x80x2 formed around the auxiliary round plate 3xe2x80x3 and can be rotated. Center apertures, 4, 4xe2x80x2 and 4xe2x80x3 which mate with a center aperture 4xe2x80x3xe2x80x2 of the rotary plate 11 are locked with a bushing 5, and a gap formed between portions A and B positioned in one direction of the flange 11xe2x80x2 is used with an operating part 13 of the rotary plate 11. One end of a tension spring 14 is mounted in an aperture 13xe2x80x2 of the operating part 13. Locking rods 8 and 8xe2x80x2 of a locking handle 7 extend into apertures 15 and 16 and locking apertures 9 and 9xe2x80x2 by pressure from a press part 18 having a press axle 6 with a spring 17 surrounding press axle 6. At the same time, the operating part 13 which is rotatably biased in the direction of portion A, provides that the locking rods 8 and 8xe2x80x2 smoothly enter along inclined planes 16xe2x80x2 of the apertures 16.
Since an operation of the hinge for the collapsible ladders disclosed in the above Korean Utility Model Registration has been already known, and also its structure does not include a characterized portion of the present invention, a detailed description thereof shall be omitted.
The hinge for the collapsible ladders described above has problems that may cause damage or breakdown of the spring due to its external exposure, and further, hands or gloves of an operator may be jammed in the spring when the press part is pressed.
In order to solve the above problems, it is an object of the present invention to provide a hinge for collapsible ladders having a safety structure which can inwardly house a hinge spring for the collapsible ladders, prevent any damage or breakdown of the spring, and keep an operator safe during use of the ladder.
To accomplish the above object of the present invention, a hinge for collapsible ladders, includes an external frame including a center aperture and a pair of locking apertures; an inner frame including a center aperture and a plurality of pairs of locking apertures, the inner frame being rotatably movable relative to the external frame around the center apertures; a rotary plate rotatably disposed between the inner frame and the external frame and having locking apertures therein; a substantially flat rotary spring having one end mounted to the inner frame and an opposite end mounted to the rotary plate to impart a turning force to the rotary plate; a hub member rotatably connecting the inner frame and the external frame about the center apertures, and supporting the frames, the hub member including a locking end at one side thereof; a locking part having a locking end for extension into the locking apertures of the external and inner frames to fix an angle of the inner frame and the external frame relative to each other; a press axle connected with the locking part and passing through the hub member, the press axle including a spring bearing end; and a spring positioned between the locking end of the hub member and the bearing end of the press axle.